JPH01264822A - Molding method for optical disc board containing preformat and die to be used for that - Google Patents

Abstract

PURPOSE:To prevent deterioration of transfer properties ascribable to a flow phenomenon of a pit, by a method wherein at the time of release of a molded optical disc board, priority is given to that of the surface of a split mold corresponding to an uneven surface part. CONSTITUTION:A movable mold 1 is provided with a stamper 4, external circumferential ring 5, spring 16 pressing them in the direction of mold break and an air conducting hole 9 and a tapered surface 10 expanded in the direction of the mold break is formed on an inner circumferential surface of the ring 5. At the time of mold break, the ring 5 is pushed up by (t) from a parting line 8 by the spring 16. The (t) is made slightly smaller than a gap (t') between a holding part of the external circumferential ring 5 and the stamper 4. Although air is blown off through an air blow ejector at the time of mold break after cooling and solidification of injected resin 11, the ring 5 is extruded by the (t), a molded board is held by the tapered surface 10 and released from a stamper surface. Then, when the die is broken at least the (t), the molded board is released from a stationary mold through an air blow of the stationary mold and the board is held under a floated state from the stamper surface. After the die is broken completely, the board is released completely through mechanical ejection further.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention is applicable to ROM discs such as CDs and VDs, DRAW discs, etc.
The present invention relates to a method of injection molding a plastic substrate for a high-density information recording carrier such as an optical disk such as a disk or an E-DRAD disk or an optical card, and a mold used therein.

BACKGROUND OF THE INVENTION Substrates for high-density information recording carriers such as the above-mentioned optical disks are generally made of glass, metal, ceramics, or plastics, and plastics are preferred from the viewpoint of lightness, strength, and productivity.

However, the plastic substrate used in the optical discs mentioned above is extremely thin and flat, with a thickness of about 1.2 to 1.5 mm and a maximum diameter of about 300 m [Il], and the material is generally made of acrylic, which has poor fluidity. Since resin or polycarbonate resin is used, it is difficult to injection mold a plastic substrate that completely satisfies optical properties such as birefringence and moldability such as transferability at the same time.

Among the various performances required of this type of disk substrate, one of the most important factors is the transfer performance for accurately transferring the surface shape of the stamper placed in the mold, that is, the information pit array.

Conventionally, a mold for injection molding a plastic substrate for an optical disk generally has a structure as shown in FIG. 2.3.

The mold shown in FIG. 2 has a molding cavity 3 formed by a pair of mold parts or split molds, for example a movable mold 1 and a fixed mold 2, and a part of the surface of the molding cavity (in the figure A stamper 4 having submicron-order information bits, tracks, etc. on its surface is attached to the surface of the movable mold 10 by a stamper holder 5. Further, an outer peripheral ring 6 is attached on the surface of the fixed molding cavity. The resin is injected into the mold cavity 3 via the sprue 7.

FIG. 3 shows another conventional injection mold. In FIG. 3, dashes are added to members corresponding to those in FIG. 2. The injection mold shown in FIG. 3 eliminates the outer peripheral ring 6 of FIG.
9 come into contact with each other to define the outer peripheral end surface of the molding cavity. This type of mold is generally called a spigot mold.

To explain the method of molding a disk substrate using the mold shown in Fig. 2, first, when installing the mold of an injection molding machine (not shown), the fixed mold 2 is mounted on the fixed platen, and the movable mold 1 is mounted on the movable platen. is installed. During molding, after the movable mold and fixed mold are closed, molten resin is injected into the cavity 3 through the sprue 7. After that, the resin melted and injected into the cavity is cooled and solidified for a certain period of time, and then the mold clamping mechanism is driven to separate the movable mold from the fixed mold and open the mold.At the same time, air is generated near the center of the fixed mold. Air is blown out from the ejector to release the molded substrate from the fixed mirror surface.

Therefore, the molded plastic substrate is opened while being attached to the movable mirror surface, that is, the surface of the stamper 4. Next, after the mold is completely opened, air is blown out from another air ejector installed near the center of the movable mold to separate the stamper and the substrate, and the substrate is further ejected using a mechanical ejector rod. By doing so, the substrate is completely released from the mold.

Problems to be Solved by the Invention There are two types of optical discs: pre-format and post-format.

In the case of the preformat method, only groups (continuous grooves) that will serve as guide tracks are molded onto a plastic substrate for optical discs, and the necessary format is obtained by attaching a recording film to the thus obtained grooved plastic substrate. Written after the optical disc is installed in the drive. Therefore, in order to mold the substrate, it is only necessary to accurately transfer the group from a stamper.

However, in recent years, in addition to the uneconomical nature of the post-format method, due to advances in mask ring or drive design technology, the so-called pre-format method has become mainstream, in which the format is inserted at the same time as the group at the plastic substrate molding stage. . This preformatted signal is
Unlike the above-mentioned continuous guide track, it is composed of pits with a fixed length.

The preformat signal is generally cut into a stamper using the mask ring method, but when the stamper containing this preformat signal was molded using the conventional mold according to the above procedure, pit circles that were not seen in the group parts were found. A "flow phenomenon" occurs in the circumferential direction, that is, a phenomenon in which the uneven shape of the plastic substrate transferred and molded from the stamper "sags" and the transfer is not performed accurately.

Evaluation of the recording characteristics of optical disk substrates in which this phenomenon occurs, in which a recording film is attached to a plastic substrate, has an adverse effect on the amount of reflected light, and ultimately on the recording and reproducing characteristics.

As a result of intensive study on this phenomenon, the present inventors discovered that the above phenomenon occurs between the time the mold is opened and the time the molded disk substrate is released from the stamper surface, and a method for solving this problem was found. invented.

Therefore, the object of the present invention is to solve the above-mentioned "flow phenomenon" of the pit.
The object of the present invention is to provide a method for solving the problem of deterioration in transferability caused by the problem, and a mold assembly used therein.

Means for Solving the Problems The method of molding a plastic substrate for an optical disk provided by the present invention includes a step of supplying a liquid resin into a molding cavity formed by a pair of split molds, and the molded optical disk substrate is The present invention is characterized in that when releasing the mold from the pair of split molds, the molded optical disk substrate is released first from the split mold surface corresponding to at least the uneven surface portion.

The above-mentioned molding method generally employs an injection molding method, and therefore, the above-mentioned liquid resin is generally a thermoplastic molten resin, but it can also be applied to other methods such as compression molding and casting.

The uneven surface portion may be formed by a stamper attached to one of the mold halves, and is generally a submicron replica surface corresponding to a continuous guide track and/or preformat signal.

When releasing the mold, it is preferable to inject a fluid between the molded optical disk substrate and the surface of the split mold.

The mold assembly for molding a plastic substrate for an optical disk provided by the present invention has a pair of opposing inner surfaces defined by a pair of split molds, and a ring-shaped mold assembly attached to the outer circumference of one of the split molds. a molded cavity defined by an inner surface of the member, one of the pair of mutually opposing inner surfaces having a mirror surface and the other inner surface for transferring information pits to the molded disk; The inner surface of the ring-shaped member is a tapered surface that expands in the direction of taking out the molded product, and the ring-shaped member is slidable in the mold opening direction. It is characterized by

The pair of inner surfaces constituting the cavity can be of a spigot type.

The ring-shaped member constituting the female mold can hold the stamper.

Preferably, a deaeration hole is formed in the ring-shaped member.

Function: A case in which an optical disc substrate is molded by the conventional method as described above will be explained.

The molten resin injected into the cavity tries to contract in the circumferential direction as it cools, but while the mold is closed, it is held down by the pressing force from the mold and the friction with the mold surface. Therefore, stress is generated but no contraction occurs.

Next, when the mold begins to open and the signal surface of the substrate is still in close contact with the stamper, when the surface of the molded substrate opposite to the signal surface separates from the mold, that surface of the substrate will move toward the inner circumference. It starts to contract. At this point, since the signal surface of the substrate is still in close contact with the stamper, this signal surface tends to be held as it is by the frictional force with the stamper surface. However, since the shrinkage force of the resin is greater, it is dragged until the point where the forces are balanced.

The "flow phenomenon" of pits is, so to speak, a mark left on the molded substrate by the pits of the stamper, which is caused by the difference in shrinkage rate between the stamper and the disk substrate. Therefore, this phenomenon affects the height of the pit, the higher the pit, the longer the flow distance.

From the above analysis, the inventors thought that in order to solve this phenomenon, it would be best to release the signal surface of the substrate from the stamper before it was dragged by the opposite surface, and thus completed the present invention. .

Preferred embodiments of the present invention will be described below with reference to the accompanying drawings, but the present invention is not limited thereto.

Embodiment FIG. 1 is a conceptual sectional view of a mold according to a preferred embodiment of the present invention.

In the mold assembly shown in FIG. 1, 1 is a movable mold, 2 is a fixed mold, 3 is a molding cavity, and 4 is a stamper 15 having a guide group and/or a format signal pit on its surface, which is held by the movable mold. 16 is a pressing spring that presses the outer ring in the mold opening direction, 7
8 is a sprue, 8 is a parting line, 9 is a conduction hole for escaping air in the cavity, and 10 is a tapered surface formed on the inner peripheral surface of the outer ring 5 and enlarged toward the mold opening direction.

Hereinafter, the sequence of operations when actually molding is performed using the mold shown in FIG. 1 will be explained using conceptual diagrams shown in FIGS. 4 to 7.

First, FIG. 4 shows a state in which a movable mold 1 and a fixed mold 2 are attached to a movable plate and a fixed plate, respectively, of a molding machine (not shown), and the molds are opened. At this time, the outer ring 5 is pushed up by a length t from the parting line 8 by the pressing spring 16. This length t is the outer ring 5
The clearance t' between the holding portion of the stamper 4 and the stamper 4 is set to be smaller than the clearance t' by 0 to 40 μm, ideally by 5 to 20 μm.

Next, Fig. 5 shows that the movable mold and the fixed mold are closed, and the molten resin 1
1 is injected and filled into the cavity.

At this time, the outer ring 5 comes into contact with the fixed mold and is pushed into the movable mold by the distance t.

Next, FIG. 6 shows the resin 1 melted and injected into the cavity.
FIG. 2 is a diagram showing the state at the start of a mold opening operation for taking out the molded plastic disk from the mold after the molded plastic disk has been cooled and solidified for a certain period of time.

At the start of this mold opening operation, air is blown out through an air blow ejector (not shown) installed near the center of the movable mold in order to release the molded plastic substrate, but at the same time While the mold is opened by the distance t, the outer ring 5 is pushed out by the pressing spring 16. Since the inner circumferential surface of the outer ring 5 is formed with a tapered surface IO that expands toward the mold opening direction, the molded plastic substrate is formed on the tapered surface 10.
The mold is released from the stamper surface while the outer periphery is held by the stamper.

Next, when the mold is opened by more than the above distance, the fixed mold and the molded plastic substrate are separated from each other by air blowing of the fixed mold, and the molded substrate is transferred to the movable mold with a stamper as shown in Fig. 7. -Hold it above the surface.

After the mold is completely opened, the molded plastic substrate is completely released from the mold using a mechanical ejection ring, rod, or the like.

Note that the air blowing operation described above is performed simultaneously with the movable air blow ejector described above, and is also supplied between the plastic substrate and the fixed mold via an air blow ejector (not shown) installed near the center of the fixed mold. However, it is necessary to release the molded plastic substrate from the stamper side first.

Preferably, at the initial stage of mold opening as shown in FIG. 6, the air blow ejector of the fixed mold is stopped, and after the mold has opened by a distance t, air is blown out from the air blow ejector of the fixed mold. It is more effective to do so. Further, in this case, since the air supplied from the movable air blow ejector flows out from the air escape passage hole 9, the disk substrate held by the outer ring 5 will not come off due to pressure.

FIG. 8 shows an electron micrograph of the bit portion of the plastic disk substrate molded in this manner. Comparing this with Figure 9, which shows an electron micrograph of the same part molded with a conventional mold, it is clear that the mold of the present invention has less misalignment, or "flow," in the bit part. I understand that.

Effects By using the method of the present invention, the "flow" phenomenon is eliminated as described above, and at the same time, the following effects are also achieved.

(1) Since the signal surface is released from the mold at the same time as the mold is opened, the entire signal surface shrinks uniformly. Therefore, the roundness of the group is improved.

(2) Furthermore, since the signal surface is released from the mold at the same time as the mold is opened, and therefore the unbalance of mold release is eliminated, CD
This eliminates the gaseous pattern known as cladding, which is a problem.

[Brief explanation of the drawing]

FIG. 1 is a conceptual cross-sectional view of an injection mold assembly used for molding a plastic substrate for an optical disk according to an embodiment of the present invention. 2 and 3 are conceptual cross-sectional views of an injection mold assembly used for molding a conventionally known plastic substrate for an optical disk. 4 to 7 are explanatory diagrams of each process when molding a plastic substrate for an optical disk using the injection mold assembly shown in FIG. 1. FIG. 8 is a copy of an electron micrograph of a bit portion of a plastic disk substrate molded according to the present invention. FIG. 9 is a reproduction of an electron micrograph of a bit portion of a plastic disk substrate molded by a conventional method. (Symbols in the figure) 1...Movable type, 2...Fixed type, 3...Molding cavity, 4...Skumper, 5...Outer ring, 7. Pipe sprue, 8... parting line,

Claims (7)

[Claims] (1) In a method for molding a plastic substrate for an optical disc having an uneven surface portion on one side, which includes a step of supplying liquid resin into a molding cavity formed by a pair of split molds, the molded optical disc substrate is placed between the pair of split molds. A method characterized in that when releasing the molded optical disk substrate from the mold, the molded optical disk substrate is released first from the split mold surface corresponding to at least the uneven surface portion. 2. The method according to claim 1, wherein said uneven surface portion is constituted by a stamper attached to one of said split molds. (3) The method according to claim 1 or 2, wherein a fluid is injected between the molded optical disk substrate and the surface of the split mold during the mold release. (4) It has a molding cavity defined by a pair of mutually opposing inner surfaces defined by a pair of split molds and an inner surface of a ring-shaped member attached to an outer peripheral portion of one of the split molds. One of the pair of inner surfaces facing each other is a mirror surface, and the other inner surface is an uneven surface for transferring information pits to the molded disk, and the inner surface of the ring-shaped member In a mold assembly for molding a plastic substrate for optical disks, which has a tapered surface that expands toward the direction in which the molded product is taken out, the above-mentioned ring-shaped member is slidable in the mold opening direction. Characteristic mold assembly. (5) The mold assembly according to claim 4, wherein the pair of inner surfaces constituting the cavity are of a spigot type. (6) The mold assembly according to claim 4 or 5, wherein the ring-shaped member constituting the female mold holds a stamper. (7) The mold assembly according to any one of claims 4 to 6, wherein a deaeration hole is formed in the ring-shaped member.